The present invention generally relates to unmanned aerial vehicles and airships and, more particularly, to a hybrid airship having the shape of delta-wing and to a method for using the delta-winged hybrid airship as an unmanned airborne communications relay platform.
To enhance intelligence-gathering, surveillance, reconnaissance, and communications relay it would be useful to have unmanned aerial vehicles available that can operate at very high altitudes and that have a high endurance. The capability to operate at very high altitudes is desirable to make the platform survivable against anti-aircraft threats, to maximize the line-of-sight radius for sensors and communications equipment, and to place the aircraft above the effects of atmospheric weather system. One of the challenges of designing a fixed wing aircraft to cruise at high altitudes is the achievement of a low structural weight. Such aircraft require large wing areas due to the very low density of air at high altitudes, so that the wing weight becomes a key design driver. A possible alternative to fixed wing aircraft is to carry the payload in a lighter-than-air vehicle, such as an airship, but very large volume gas envelopes are needed to achieve neutral buoyancy at high altitudes. Therefore, these lighter-than-air vehicles are large and heavy, which limits the altitude at which the vehicles can operate.
Furthermore, there is a need for airborne platforms that are able to carry high power directed energy devices as a payload and that can operate as communications relay platforms. It is further desirable, to operate such airborne platform at high altitudes out of reach for anti-aircraft threats and above the effects of atmospheric weather systems. In order to be effective, it is still further desirable that such airborne platforms have a high endurance. High power directed energy devices, such as large area electromagnetic antennas, usually have a very large circular or elliptical shape. Therefore, aerial vehicles carrying such devices need to provide a large wing area in which the devices can be integrated which may limit the operational altitude as well as the endurance of the aerial vehicle.
Prior art unmanned aerial vehicles include, for example, the Global Hawk, a high altitude, long-endurance unmanned aerial vehicle used by the US Air Force as a surveillance aircraft. The Global Hawk air vehicle is to provide high resolution synthetic aperture radar that can penetrate cloud-cover and sandstorms and electro-optical/infrared imagery at long range with long loiter times over target areas. The Global Hawk is capable of both wideband satellite and line-of-sight data link communications. The capabilities of the Global Hawk allow more precise targeting of weapons and better protection of forces through superior surveillance capabilities. However, while being a unmanned aircraft, the Global Hawk still is a reusable heavier-than-air craft using fossil fuels. The power output of conventional combustion engines and turbines decreases drastically at high altitudes because of the corresponding decrease in density of air, which is necessary to maintain the combustion of fossil fuels. A runway is needed for launching the Global Hawk and for the landing. The Global Hawk has an operating range of up to 3000 nautical miles from its launch area, with its loiter capability over the target area limited to about 24 to 36 hours at altitudes of about 60,000 to 66,000 feet. The operating range, the loiter time over a target area, and the altitude of the global hawk are limited since the Global Hawk still is an conventional heavier-than-air aircraft using fossil fuels. For future reconnaissance missions, unmanned aerial vehicles with even longer loiter capabilities over a target area at even higher altitudes are desired.
Concepts have been disclosed for futuristic unmanned aircraft missions that reach beyond the standard intelligence-gathering mission to very long-range strike, vertical operations, and ultra-long-endurance surveillance. One advanced concept was reported, for example, by David A. Fulghum in Aviation Week & Space Technology, Oct. 20, 2003, page 70. This article describes an unmanned aerial vehicle disclosed by the Northrop-Grumman Unmanned Systems group in Rancho Bernardo, Calif. To optimize the benefit of flying without a crew, a four-engine Ultra-Hale (high-altitude, long-endurance) unmanned aerial vehicle is disclosed that is designed to stay aloft for three months with a surveillance sensor payload. Designed as a wing filled with a combination of hydrogen and helium to achieve zero buoyancy, the aircraft can be launched without a conventional runway. By using the explosive gas hydrogen, the disclosed aerial vehicle may not be safe to operate and prone to accidents. Once aloft, the aircraft takes about half a day using its combination powerplants (involving solar energy and fuel cells) to climb to an operating altitude of 80,000–120,000 ft. However, the endurance of the described flying wing aircraft and therefore of reconnaissance missions would be limited by the reliability and lifetime of the fuel cells, even if the fuel cells are supplemented by solar panels. Furthermore, endurance longer than the three months said to be reached by described flying wing aircraft is desirable.
The article by David A. Fulghum also discloses a delta-winged unmanned aircraft for strike/reconnaissance missions that can be launched from small-deck ships without catapults and arresting gear. While being able to takeoff and land vertically, the disclosed delta-winged unmanned aircraft is still an conventional aircraft depending an fossil fuels as an energy source. Consequently, the endurance of the delta-winged aircraft is limited by the amount of fuel that can be carried.
As can be seen, there is a need for an unmanned aerial vehicle that has a large enough wing area to carry high power directed energy devices as a payload, that has a high endurance, and that can be operated at very high altitudes. Furthermore, there is a need for an unmanned aerial vehicle that does not depend on conventional runways for launching and landing. Also, there is a need for an airborne platform that can be used for intelligence-gathering, surveillance, reconnaissance, and communications relay missions over an extended period of time and at altitudes high enough to make the aerial vehicle survivable against anti-aircraft threats, to maximize the line-of-sight radius for sensors and communications equipment, and to place the aerial vehicle above the effects of atmospheric weather system. There has also arisen a need to provide an unmanned aerial vehicle that is capable of carrying high power directed energy devices and of operating at very high altitudes for flights of long durations. There has further arisen a need to provide an unmanned aerial vehicle that uses a propulsion system that is independent from fossil fuels and fuel cells and, therefore, does not limit the flight endurance of the aerial vehicle. There has also arisen a need to provide an aerial vehicle, such as a hybrid airship, that combines the advantages of heavier-than-air technology and lighter-than-air technology.